OK, let's work through this together. We're starting with 10 and we're going to multiply it by 391, which means we add 10 to itself 391 times.
Step 1: 0 + 10 = 10
Step 2: 10 + 10 = 20
Step 3: 20 + 10 = 30
Step 4: 30 + 10 = 40
Step 5: 40 + 10 = 50
Step 6: 50 + 10 = 60
Step 7: 60 + 10 = 70
Step 8: 70 + 10 = 80
Step 9: 80 + 10 = 90
Step 10: 90 + 10 = 100
Step 11: 100 + 10 = 110
Step 12: 110 + 10 = 120
Step 13: 120 + 10 = 130
Step 14: 130 + 10 = 140
Step 15: 140 + 10 = 150
Step 16: 150 + 10 = 160
Step 17: 160 + 10 = 170
Step 18: 170 + 10 = 180
Step 19: 180 + 10 = 190
Step 20: 190 + 10 = 200
Step 21: 200 + 10 = 210
Step 22: 210 + 10 = 220
Step 23: 220 + 10 = 230
Step 24: 230 + 10 = 240
Step 25: 240 + 10 = 250
Step 26: 250 + 10 = 260
Step 27: 260 + 10 = 270
Step 28: 270 + 10 = 280
Step 29: 280 + 10 = 290
Step 30: 290 + 10 = 300
Step 31: 300 + 10 = 310
Step 32: 310 + 10 = 320
Step 33: 320 + 10 = 330
Step 34: 330 + 10 = 340
Step 35: 340 + 10 = 350
Step 36: 350 + 10 = 360
Step 37: 360 + 10 = 370
Step 38: 370 + 10 = 380
Step 39: 380 + 10 = 390
Step 40: 390 + 10 = 400
Step 41: 400 + 10 = 410
Step 42: 410 + 10 = 420
Step 43: 420 + 10 = 430
Step 44: 430 + 10 = 440
Step 45: 440 + 10 = 450
Step 46: 450 + 10 = 460
Step 47: 460 + 10 = 470
Step 48: 470 + 10 = 480
Step 49: 480 + 10 = 490
Step 50: 490 + 10 = 500
Step 51: 500 + 10 = 510
Step 52: 510 + 10 = 520
Step 53: 520 + 10 = 530
Step 54: 530 + 10 = 540
Step 55: 540 + 10 = 550
Step 56: 550 + 10 = 560
Step 57: 560 + 10 = 570
Step 58: 570 + 10 = 580
Step 59: 580 + 10 = 590
Step 60: 590 + 10 = 600
Step 61: 600 + 10 = 610
Step 62: 610 + 10 = 620
Step 63: 620 + 10 = 630
Step 64: 630 + 10 = 640
Step 65: 640 + 10 = 650
Step 66: 650 + 10 = 660
Step 67: 660 + 10 = 670
Step 68: 670 + 10 = 680
Step 69: 680 + 10 = 690
Step 70: 690 + 10 = 700
Step 71: 700 + 10 = 710
Step 72: 710 + 10 = 720
Step 73: 720 + 10 = 730
Step 74: 730 + 10 = 740
Step 75: 740 + 10 = 750
Step 76: 750 + 10 = 760
Step 77: 760 + 10 = 770
Step 78: 770 + 10 = 780
Step 79: 780 + 10 = 790
Step 80: 790 + 10 = 800
Step 81: 800 + 10 = 810
Step 82: 810 + 10 = 820
Step 83: 820 + 10 = 830
Step 84: 830 + 10 = 840
Step 85: 840 + 10 = 850
Step 86: 850 + 10 = 860
Step 87: 860 + 10 = 870
Step 88: 870 + 10 = 880
Step 89: 880 + 10 = 890
Step 90: 890 + 10 = 900
Step 91: 900 + 10 = 910
Step 92: 910 + 10 = 920
Step 93: 920 + 10 = 930
Step 94: 930 + 10 = 940
Step 95: 940 + 10 = 950
Step 96: 950 + 10 = 960
Step 97: 960 + 10 = 970
Step 98: 970 + 10 = 980
Step 99: 980 + 10 = 990
Step 100: 990 + 10 = 1000
Step 101: 1000 + 10 = 1010
Step 102: 1010 + 10 = 1020
Step 103: 1020 + 10 = 1030
Step 104: 1030 + 10 = 1040
Step 105: 1040 + 10 = 1050
Step 106: 1050 + 10 = 1060
Step 107: 1060 + 10 = 1070
Step 108: 1070 + 10 = 1080
Step 109: 1080 + 10 = 1090
Step 110: 1090 + 10 = 1100
Step 111: 1100 + 10 = 1110
Step 112: 1110 + 10 = 1120
Step 113: 1120 + 10 = 1130
Step 114: 1130 + 10 = 1140
Step 115: 1140 + 10 = 1150
Step 116: 1150 + 10 = 1160
Step 117: 1160 + 10 = 1170
Step 118: 1170 + 10 = 1180
Step 119: 1180 + 10 = 1190
Step 120: 1190 + 10 = 1200
Step 121: 1200 + 10 = 1210
Step 122: 1210 + 10 = 1220
Step 123: 1220 + 10 = 1230
Step 124: 1230 + 10 = 1240
Step 125: 1240 + 10 = 1250
Step 126: 1250 + 10 = 1260
Step 127: 1260 + 10 = 1270
Step 128: 1270 + 10 = 1280
Step 129: 1280 + 10 = 1290
Step 130: 1290 + 10 = 1300
Step 131: 1300 + 10 = 1310
Step 132: 1310 + 10 = 1320
Step 133: 1320 + 10 = 1330
Step 134: 1330 + 10 = 1340
Step 135: 1340 + 10 = 1350
Step 136: 1350 + 10 = 1360
Step 137: 1360 + 10 = 1370
Step 138: 1370 + 10 = 1380
Step 139: 1380 + 10 = 1390
Step 140: 1390 + 10 = 1400
Step 141: 1400 + 10 = 1410
Step 142: 1410 + 10 = 1420
Step 143: 1420 + 10 = 1430
Step 144: 1430 + 10 = 1440
Step 145: 1440 + 10 = 1450
Step 146: 1450 + 10 = 1460
Step 147: 1460 + 10 = 1470
Step 148: 1470 + 10 = 1480
Step 149: 1480 + 10 = 1490
Step 150: 1490 + 10 = 1500
Step 151: 1500 + 10 = 1510
Step 152: 1510 + 10 = 1520
Step 153: 1520 + 10 = 1530
Step 154: 1530 + 10 = 1540
Step 155: 1540 + 10 = 1550
Step 156: 1550 + 10 = 1560
Step 157: 1560 + 10 = 1570
Step 158: 1570 + 10 = 1580
Step 159: 1580 + 10 = 1590
Step 160: 1590 + 10 = 1600
Step 161: 1600 + 10 = 1610
Step 162: 1610 + 10 = 1620
Step 163: 1620 + 10 = 1630
Step 164: 1630 + 10 = 1640
Step 165: 1640 + 10 = 1650
Step 166: 1650 + 10 = 1660
Step 167: 1660 + 10 = 1670
Step 168: 1670 + 10 = 1680
Step 169: 1680 + 10 = 1690
Step 170: 1690 + 10 = 1700
Step 171: 1700 + 10 = 1710
Step 172: 1710 + 10 = 1720
Step 173: 1720 + 10 = 1730
Step 174: 1730 + 10 = 1740
Step 175: 1740 + 10 = 1750
Step 176: 1750 + 10 = 1760
Step 177: 1760 + 10 = 1770
Step 178: 1770 + 10 = 1780
Step 179: 1780 + 10 = 1790
Step 180: 1790 + 10 = 1800
Step 181: 1800 + 10 = 1810
Step 182: 1810 + 10 = 1820
Step 183: 1820 + 10 = 1830
Step 184: 1830 + 10 = 1840
Step 185: 1840 + 10 = 1850
Step 186: 1850 + 10 = 1860
Step 187: 1860 + 10 = 1870
Step 188: 1870 + 10 = 1880
Step 189: 1880 + 10 = 1890
Step 190: 1890 + 10 = 1900
Step 191: 1900 + 10 = 1910
Step 192: 1910 + 10 = 1920
Step 193: 1920 + 10 = 1930
Step 194: 1930 + 10 = 1940
Step 195: 1940 + 10 = 1950
Step 196: 1950 + 10 = 1960
Step 197: 1960 + 10 = 1970
Step 198: 1970 + 10 = 1980
Step 199: 1980 + 10 = 1990
Step 200: 1990 + 10 = 2000
Step 201: 2000 + 10 = 2010
Step 202: 2010 + 10 = 2020
Step 203: 2020 + 10 = 2030
Step 204: 2030 + 10 = 2040
Step 205: 2040 + 10 = 2050
Step 206: 2050 + 10 = 2060
Step 207: 2060 + 10 = 2070
Step 208: 2070 + 10 = 2080
Step 209: 2080 + 10 = 2090
Step 210: 2090 + 10 = 2100
Step 211: 2100 + 10 = 2110
Step 212: 2110 + 10 = 2120
Step 213: 2120 + 10 = 2130
Step 214: 2130 + 10 = 2140
Step 215: 2140 + 10 = 2150
Step 216: 2150 + 10 = 2160
Step 217: 2160 + 10 = 2170
Step 218: 2170 + 10 = 2180
Step 219: 2180 + 10 = 2190
Step 220: 2190 + 10 = 2200
Step 221: 2200 + 10 = 2210
Step 222: 2210 + 10 = 2220
Step 223: 2220 + 10 = 2230
Step 224: 2230 + 10 = 2240
Step 225: 2240 + 10 = 2250
Step 226: 2250 + 10 = 2260
Step 227: 2260 + 10 = 2270
Step 228: 2270 + 10 = 2280
Step 229: 2280 + 10 = 2290
Step 230: 2290 + 10 = 2300
Step 231: 2300 + 10 = 2310
Step 232: 2310 + 10 = 2320
Step 233: 2320 + 10 = 2330
Step 234: 2330 + 10 = 2340
Step 235: 2340 + 10 = 2350
Step 236: 2350 + 10 = 2360
Step 237: 2360 + 10 = 2370
Step 238: 2370 + 10 = 2380
Step 239: 2380 + 10 = 2390
Step 240: 2390 + 10 = 2400
Step 241: 2400 + 10 = 2410
Step 242: 2410 + 10 = 2420
Step 243: 2420 + 10 = 2430
Step 244: 2430 + 10 = 2440
Step 245: 2440 + 10 = 2450
Step 246: 2450 + 10 = 2460
Step 247: 2460 + 10 = 2470
Step 248: 2470 + 10 = 2480
Step 249: 2480 + 10 = 2490
Step 250: 2490 + 10 = 2500
Step 251: 2500 + 10 = 2510
Step 252: 2510 + 10 = 2520
Step 253: 2520 + 10 = 2530
Step 254: 2530 + 10 = 2540
Step 255: 2540 + 10 = 2550
Step 256: 2550 + 10 = 2560
Step 257: 2560 + 10 = 2570
Step 258: 2570 + 10 = 2580
Step 259: 2580 + 10 = 2590
Step 260: 2590 + 10 = 2600
Step 261: 2600 + 10 = 2610
Step 262: 2610 + 10 = 2620
Step 263: 2620 + 10 = 2630
Step 264: 2630 + 10 = 2640
Step 265: 2640 + 10 = 2650
Step 266: 2650 + 10 = 2660
Step 267: 2660 + 10 = 2670
Step 268: 2670 + 10 = 2680
Step 269: 2680 + 10 = 2690
Step 270: 2690 + 10 = 2700
Step 271: 2700 + 10 = 2710
Step 272: 2710 + 10 = 2720
Step 273: 2720 + 10 = 2730
Step 274: 2730 + 10 = 2740
Step 275: 2740 + 10 = 2750
Step 276: 2750 + 10 = 2760
Step 277: 2760 + 10 = 2770
Step 278: 2770 + 10 = 2780
Step 279: 2780 + 10 = 2790
Step 280: 2790 + 10 = 2800
Step 281: 2800 + 10 = 2810
Step 282: 2810 + 10 = 2820
Step 283: 2820 + 10 = 2830
Step 284: 2830 + 10 = 2840
Step 285: 2840 + 10 = 2850
Step 286: 2850 + 10 = 2860
Step 287: 2860 + 10 = 2870
Step 288: 2870 + 10 = 2880
Step 289: 2880 + 10 = 2890
Step 290: 2890 + 10 = 2900
Step 291: 2900 + 10 = 2910
Step 292: 2910 + 10 = 2920
Step 293: 2920 + 10 = 2930
Step 294: 2930 + 10 = 2940
Step 295: 2940 + 10 = 2950
Step 296: 2950 + 10 = 2960
Step 297: 2960 + 10 = 2970
Step 298: 2970 + 10 = 2980
Step 299: 2980 + 10 = 2990
Step 300: 2990 + 10 = 3000
Step 301: 3000 + 10 = 3010
Step 302: 3010 + 10 = 3020
Step 303: 3020 + 10 = 3030
Step 304: 3030 + 10 = 3040
Step 305: 3040 + 10 = 3050
Step 306: 3050 + 10 = 3060
Step 307: 3060 + 10 = 3070
Step 308: 3070 + 10 = 3080
Step 309: 3080 + 10 = 3090
Step 310: 3090 + 10 = 3100
Step 311: 3100 + 10 = 3110
Step 312: 3110 + 10 = 3120
Step 313: 3120 + 10 = 3130
Step 314: 3130 + 10 = 3140
Step 315: 3140 + 10 = 3150
Step 316: 3150 + 10 = 3160
Step 317: 3160 + 10 = 3170
Step 318: 3170 + 10 = 3180
Step 319: 3180 + 10 = 3190
Step 320: 3190 + 10 = 3200
Step 321: 3200 + 10 = 3210
Step 322: 3210 + 10 = 3220
Step 323: 3220 + 10 = 3230
Step 324: 3230 + 10 = 3240
Step 325: 3240 + 10 = 3250
Step 326: 3250 + 10 = 3260
Step 327: 3260 + 10 = 3270
Step 328: 3270 + 10 = 3280
Step 329: 3280 + 10 = 3290
Step 330: 3290 + 10 = 3300
Step 331: 3300 + 10 = 3310
Step 332: 3310 + 10 = 3320
Step 333: 3320 + 10 = 3330
Step 334: 3330 + 10 = 3340
Step 335: 3340 + 10 = 3350
Step 336: 3350 + 10 = 3360
Step 337: 3360 + 10 = 3370
Step 338: 3370 + 10 = 3380
Step 339: 3380 + 10 = 3390
Step 340: 3390 + 10 = 3400
Step 341: 3400 + 10 = 3410
Step 342: 3410 + 10 = 3420
Step 343: 3420 + 10 = 3430
Step 344: 3430 + 10 = 3440
Step 345: 3440 + 10 = 3450
Step 346: 3450 + 10 = 3460
Step 347: 3460 + 10 = 3470
Step 348: 3470 + 10 = 3480
Step 349: 3480 + 10 = 3490
Step 350: 3490 + 10 = 3500
Step 351: 3500 + 10 = 3510
Step 352: 3510 + 10 = 3520
Step 353: 3520 + 10 = 3530
Step 354: 3530 + 10 = 3540
Step 355: 3540 + 10 = 3550
Step 356: 3550 + 10 = 3560
Step 357: 3560 + 10 = 3570
Step 358: 3570 + 10 = 3580
Step 359: 3580 + 10 = 3590
Step 360: 3590 + 10 = 3600
Step 361: 3600 + 10 = 3610
Step 362: 3610 + 10 = 3620
Step 363: 3620 + 10 = 3630
Step 364: 3630 + 10 = 3640
Step 365: 3640 + 10 = 3650
Step 366: 3650 + 10 = 3660
Step 367: 3660 + 10 = 3670
Step 368: 3670 + 10 = 3680
Step 369: 3680 + 10 = 3690
Step 370: 3690 + 10 = 3700
Step 371: 3700 + 10 = 3710
Step 372: 3710 + 10 = 3720
Step 373: 3720 + 10 = 3730
Step 374: 3730 + 10 = 3740
Step 375: 3740 + 10 = 3750
Step 376: 3750 + 10 = 3760
Step 377: 3760 + 10 = 3770
Step 378: 3770 + 10 = 3780
Step 379: 3780 + 10 = 3790
Step 380: 3790 + 10 = 3800
Step 381: 3800 + 10 = 3810
Step 382: 3810 + 10 = 3820
Step 383: 3820 + 10 = 3830
Step 384: 3830 + 10 = 3840
Step 385: 3840 + 10 = 3850
Step 386: 3850 + 10 = 3860
Step 387: 3860 + 10 = 3870
Step 388: 3870 + 10 = 3880
Step 389: 3880 + 10 = 3890
Step 390: 3890 + 10 = 3900
Step 391: 3900 + 10 = 3910

So, 10*391 = 3910